Dense Breasts Leading Risk Factor for Breast Cancer

Women with dense breast tissue instead of fat may have a higher likelihood of developing breast cancer, a recent study suggests.
For the study, researchers analyzed data of more than 18,000 women with breast cancer and 184,000 women the same age who didn’t have breast cancer. They found breast density appeared to be the biggest indicator of cancer risk, even higher than other common risk factors, including family history or waiting until after age 30 to have babies.
“Women with dense breasts have a roughly two-fold higher breast cancer risk relative to women with non-dense breasts,” said lead study author Natalie Engmann of the University of California, San Francisco.
This is disturbing because 60 percent of younger women have dense breasts, as do 40 percent of older women who have gone through menopause. Dense breasts make tumors harder to detect on mammograms, Engmann said.
“Our findings suggest that because breast density is a strong, common risk factor that can be modified, reducing the number of women with dense breasts may prevent a substantial proportion of breast cancer cases,” she told Reuters.
In the study, researchers examined data on women with four categories of breast density: almost entirely fat, mostly fat with some dense tissue, moderately dense and predominantly dense. Then, they studied several known breast cancer risk factors—a woman’s weight, family history of breast cancer, personal history of benign biopsy results, breast density and having a first baby after age 30.
They found that about 39 percent of breast cancer cases in pre-menopausal women and 26 percent of cases after menopause might be prevented if women in the two highest breast-density categories had less dense breast tissue.
But women can’t reduce their breast density, so what do the experts suggest? (The drug tamoxifen reduces cancer risk and breast density, but it comes with serious side effects and generally isn’t recommended.)
The answer is complicated. Weight gain adds fatty tissue to the breasts and lowers density, but obesity is itself a risk factor for breast cancer in older women. In fact, researchers said about 23 percent of breast cancers in older women might be prevented if overweight or obese women dropped enough weight to achieve a healthy weight.
Other common risk factors—family history and delayed childbirth—didn’t appear to explain as many cancer cases in the general population as breast density and obesity. Family history was linked to about 9 percent of cases for younger women and 8 percent in older women; delayed childbirth was connected to 9 percent of cases for younger women and 5 percent for older women.
Genetic mutations can increase the odds of breast cancer in individual women, the authors said, but this study didn’t take that risk factor into account. According to the National Cancer Institute, only 5 percent to 10 percent of breast cancers diagnosed in this country are due to inherited gene mutations.
So experts suggest women with dense breasts talk to their health-care team about screening alternatives to mammograms, especially if they have other risk factors, too. These alternatives include MRI and breast tomosynthesis, an emerging technology that has given better results than mammograms to women with dense breasts.
Women can access their individual risk using a calculator developed by the Breast Cancer Surveillance Consortium.